I've played SRK, Dantarion, and Bigfoot, and Bigfoot only managed to barely beat me on BF when I was playing poorly. SRK I do know gets to play DSF frequently.
Donkey Kong has NO options to get past G&W's D-tilt as an edgeguard. He is forced to edgeroll simply to get past this, which is punishable by a kill move. D-tilt from the platform stops him from approaching and if the G&W has any sense of spacing, he's not going to just use it when you're directly under him, but rather to hit from the "Sheik zone". The trick for G&W is that most G&Ws don't know how to buffer D-tilt from platform correctly.
D-air from the platform is also safe and likely to shield poke, and you're really not going to be beating it with Up-smash if he knows how to do platform drop -> D-air.
And nearly all the G&W players I see fail horribly at edgetrapping. This alone makes it way too easy for G&W to get a kill. You can REACT to all of Donkey Kong's ledge getups and as long as you know the <100% getup attack crosses you over on shield, he can't do **** to get up safely.
G&W is also capable of D-smashing Donkey Kong from above (more situational).
It is true that DK is limited when he is on the edge and trying to get onto the stage.
However, DK can up-b stall and bait G&W into making a mistake so that he can recover onto the stage safely. I have, however, experienced much difficulty in getting past a G&W that knows how to edge trap very well.
I have had such experiences while fighting a G&W main from LI that doesn't get to tournaments too often but he is very good- Mike G. Every time I would try to get up attack, he would d-tilt or jab to clash. And DK also has to look out for the dash attack stage spike.
Most DK's know that rolling from the edge at or under 100% is a terrible option, especially against G&W. So frankly, I don't see that as a viable recovery option unless the G&W is standing right next to the edge, allowing DK to get past him.
In times where it is imperative for DK to get back onto the stage against G&W, his best option is almost always his double jump. True, this puts him in a position to be juggled, but DK has good aerial DI and can travel across most of the stage, allowing for a position with which he can cover himself with b-airs.
In addition to what Ripple was saying, if G&W is EVER caught on a platform at around at least 55-60%, he is in position to be instantly killed by an up smash or mindgame charged up smash by baiting the spot dodge. Also, I have lost count of the amount of times I have up smashed a G&W out of d-air on a platform. The trick is to catch G&W right as he lands from d-airing fairly high above the platform. If G&W short hop d-airs on the platform, the multiple hitboxes will beat DK's attempt to up smash since the d-air is simply faster than anything DK can really do on reaction aside from shielding/avoiding it.